1. Field of the Invention
This invention relates to apparatus and methods for image data compression and decompression.
2. Description of the Prior Art
In some image data compression and decompression systems, one stage of the compression process is so-called run length and entropy encoding of the compressed data. A complementary run length and entropy decoding stage is performed at decompression.
Run length encoding involves identifying runs of a single data value (often zero) and replacing the run of data values with a single code giving the length of the run and (optionally) a terminating value.
Entropy encoding involves replacing commonly occurring bit patterns (particularly, commonly occurring data runs as mentioned above) in the compressed data with relatively short code words, and replacing less frequently occurring bit patterns in the compressed data with longer code words.
Overall, a significant and loss-less reduction in the quantity of compressed data can be achieved using these two techniques.
However, when the run length and entropy encoded code words are decompressed, even a small data error within a code word can mean that the code word cannot be decoded and so potentially a large amount of data cannot be recovered.
It is an object of the invention to provide an improved image data compression and/or decompression system.